Enclosed alkali primary batteries are used as power sources of portable type electronic devices such as portable radio sets or cassette recorders, for example.
A typical material of anodes of alkali batteries is manganese dioxide.
Recent development of various portable electronic devices is remarkable, and more and more devices need a heavy loading property. Therefore, there is a demand for a battery more excellent in high-efficiency discharge property than alkaline-manganese batteries that have been used most typically heretofore.
Conventionally known batteries include those having a spiral structure made by winding sheet-like anode, cathode and separator and injecting an electrolytic solution, and those having an inside-out structure in which a cylindrical anode, gel cathode and cylindrical separator are contained in a cylindrical metal can.
Inside-out batteries are more excellent in productivity and can provide a higher capacity at a lower cost than spiral type batteries. However, because of a small opposed area of the positive and cathodes, inside-out batteries are inferior in high-efficiency discharge property.
On the other hand, there is also known another battery excellent in high-efficiency discharge property, which is a nickel-zinc battery using a nickel oxide as the anode, zinc as the cathode and alkali salt solution as the electrolytic solution (U.K. Patent 365125).
In addition to that, this battery has a lot of advantages including (1) a high battery voltage, (2) flatness of the discharge curve and (3) high utility factor under high-rate discharge.
That battery, however, has not yet been brought into practical use.
A reason thereof is that the problems of a short lifetime caused by generation of dendrite of zinc pole in charge-discharge cycles and changes in shape have not been solved sufficiently.
There is also known an inside-out type nickel-zinc secondary battery using nickel hydroxide as the anode active material and zinc as the cathode active material (Japanese Patent Laid-Open Publication 2000-67910).
This battery, however, involves the problem that oxygen gas is generated from the anode while the charge-discharge cycle is repeated, the internal pressure of the battery rises, and the electrolytic solution may leak.
Furthermore, the theoretical capacity ratio of the positive and cathodes of this battery is 1:2. This is a remedy for preventing deterioration of the battery characteristics, such as preventing generation of a gas, and it results in leaving a large quantity of the cathode active material not used for the discharge and making it difficult to accomplish a high capacitance.
Regarding nickel-zinc primary batteries, there are almost no reports on their development.
It is therefore the first object of the invention to provide a enclosed nickel-zinc primary battery maintaining the excellent characteristics of the conventional nickel-zinc battery, having a high capacity and excellent in ratio of maintaining the capacity during its storage.
The second object of the invention is to provide an inside-out type nickel-zinc primary battery excellent in high-efficiency discharge property.
The third object of the invention is to provide a enclosed nickel-zinc primary battery having a high energy density per unit weight.
The fourth object of the invention is to provide a method of production the enclosed nickel-zinc primary battery.
The fifth object of the invention is to provide a anode used in the enclosed nickel-zinc primary battery and its production method.